FIG. 1 is a cross-sectional view of a wiring substrate 100 of a related art example. With reference to FIG. 1, the wiring substrate 100 includes a substrate body 110, a first insulating layer 120, a first conductive layer 130, a second conductive layer 140, a second insulating layer 150, a third insulating layer 160, a first external connection terminal 170, and a second external connection terminal 180.
The substrate body 110 is a part of the wiring substrate 100 serving as a base substrate on which, for example, the first conductive layer 130 is to be formed. A trench 110x and a penetration hole 110y communicating with the trench 110x are formed in the substrate body 110. The first insulating layer 120 is formed on a first surface 110a and a second surface 110b of the substrate body 110, an inner bottom surface of the trench 110x, an inner side surface of the trench 110x, and an inner side surface of the penetration hole 110y.
The first conductive layer 130 is formed on the insulating layer 120 covering the inner bottom surface and the inner side surface of the trench 110x and the inner side surface of the penetration hole 110y. The second conductive layer 140 is formed on the first conductive layer 130. The second conductive layer 140 fills the trench 110x and the penetration hole 110y. The first conductive layer 130 is electrically connected to the second conductive layer 140.
The second insulating layer 150 is formed on the first insulating layer 120 covering the first surface 110a of the substrate body 110, on a portion of the first conductive layer 130, and on a portion of the second conductive layer 140. The second insulating layer 150 includes an opening part 150x. A portion of the second conductive layer 140 is exposed at a bottom part of the opening part 150x.
The third insulating layer 160 is formed on the first insulating layer 120 covering the second surface 110b of the substrate body 110, on a portion of the first conductive layer 130, and on a portion of the second conductive layer 140. The third insulating layer 160 includes an opening part 160x. A portion of the second conductive layer 140 is exposed at a bottom part of the opening part 160x.
The first external connection terminal 170 is formed on the second conductive layer 140 exposed at the bottom part of the opening part 150x. The first external connection terminal 170 is electrically connected to the second conductive layer 140. The second external connection terminal 180 is formed on the second conductive layer 140 exposed at the bottom part of the opening part 160x. The second external connection terminal 180 is electrically connected to the second conductive layer 140.
FIGS. 2 to 4 are diagrams illustrating processes of a method for manufacturing a wiring substrate according to a related art example. First, in the process illustrated in FIG. 2, the trench 110x and the penetration hole 110y communicating with the trench 110x are formed in the substrate body 110. Then, the first insulating layer 120 is formed. The first insulating layer 120 covers the first surface 110a and the second surface 110b of the substrate body 110, the inner bottom surface and the inner side surface of the trench 110x, and the inner side surface of the penetration hole 110y. Then, a first conductive layer 1305 is formed on the first insulating layer 120 covering the first surface 110a of the substrate body 110, the inner bottom surface and the inner side surface of the trench 110x, and the inner side surface of the penetration hole 110y. The first conductive layer 130S is formed by, for example, a sputtering method. By removing an unnecessary portion of, for example, the first conductive layer 1305, the first conductive layer 130S eventually becomes the first conductive layer 130.
Then, in the process illustrated in FIG. 3, a copper plate 220 is provided on the insulating layer 120 covering the second surface 110b of the substrate body 110 via an adhesive layer 210. The adhesive layer 210 includes an opening part 210x corresponding to the penetration hole 110y. Then, a second conductive layer 140S is formed by an electroplating method using the copper plate 220 and the first conductive layer 130S as the plating power feed layer. The second conductive layer 140S fills the trench 110x and the penetration hole 110y on which the first insulating layer 120 and the first conductive layer 130S are formed. The second conductive layer 140S covers the first conductive layer 130S formed on the first surface 110a of the substrate body 110. By removing an unnecessary portion of, for example, the second conductive layer 140S, the second conductive layer 140S eventually becomes the second conductive layer 140.
Then, in the process illustrated in FIG. 4, by polishing (e.g., Chemical Mechanical Polishing, CMP) the second conductive layer 140S on the first surface 110a of the substrate body 110, the second conductive layer 140 is formed and the first conductive layer 130S becomes exposed on the first surface 110a of the substrate body 110. Then, the first conductive layer 130 is formed by removing (e.g., etching) the first conductive layer 130S exposed on the first surface 110a of the substrate body 110. Then, the adhesive layer 210 and the copper plate 220 (illustrated in FIG. 3) are removed.
Then, the second insulating layer 150, the third insulating layer 160, the first external connection terminal 170, and the second external connection terminal 180 are formed by a known method. Thereby, the manufacturing of the wiring substrate 100 is completed.    Patent Document 1: Japanese Laid-Open Patent Publication No. 2004-158537
In the above-described process illustrated in FIG. 3, the second conductive layer 140S is formed by an electroplating method using the copper plate 220 and the first conductive layer 130S as the plating power feed layer. In this process, a first plating film is grown on an inner side surface of the trench 110x toward the first conductive layer 130S. The first plating film is grown simultaneously with growing a second plating film on an inner bottom surface of the trench 110x toward the first conductive layer 130S. Further, a third plating film is grown on an inner side surface of the penetration hole 110y toward the first conductive layer 130S. The third plating film is grown simultaneously with growing a fourth plating film on an inner side surface of the penetration hole 110y toward the copper plate 220.
Accordingly, problems such as generation of seams or voids may occur at a bonding part between the above-described plating films grown in multiple directions on the second conductive layer 140S formed in the trench 110x. Further, problems such as generation of seams or voids may occur at a bonding part between the above-described plating films grown in multiple directions on the second conductive layer 140S formed in the penetration hole 110y. The generation of seams or voids tends to occur particularly when the aspect ratio with respect to the trench 110x or the penetration hole 11y becomes larger. In a case where a seam or a void is generated on the second conductive layer 140S, the second conductive layer 140S may become disconnected due to thermal stress. This may lead to a problem of degrading of connection reliability with respect to the first external connection terminal 170 or the second external connection terminal 180.